During the Mesozoic, various groups of reptiles underwent a spectacular return to an aquatic life, colonizing most marine environments. They were highly diversified both systematically and ecologically ... [more ▼]

During the Mesozoic, various groups of reptiles underwent a spectacular return to an aquatic life, colonizing most marine environments. They were highly diversified both systematically and ecologically, and most were the largest top-predators of the marine ecosystems of their time. The main groups were Ichthyosauria, Sauropterygia, Thalattosauria, and several lineages of Testudinata, Crocodyliformes, Rhynchocephalia and Squamata. Here we show that the palaeobiogeographical distribution of these marine reptiles closely followed the break-up of the supercontinent Pangaea and that they globally used the main marine corridors created by this break-up to disperse. Most Mesozoic marine reptile clades exhibit a cosmopolitan, or at least pandemic, distribution very early in their evolutionary history. The acquisition of morphological adaptations to a fully aquatic life, combined to special thermophysiological characteristics, are probably responsible for these animals to become efficient long-distance open-marine cruisers. Generally, Early Triassic taxa were near-shore animals mainly linked to the Tethys or Panthalassa coastlines. By the end of the Triassic and during the Jurassic, the break-up of Pangaea resulted in the formation of large marine corridors connecting the Tethys to the North Atlantic and Pacific realms, a trend increasing on during the Cretaceous with the expansion of the Atlantic Ocean and the break-up of the southern Gondwana, allowing open-sea marine reptiles to spread out over large distances. However, if large faunal interchanges were possible at a global scale following a dispersal model, some provinces, such as the Mediterranean Tethys, were characterized by a peculiar faunal identity, illustrating an absence of migration with time despite the apparent lack of barriers. So, if Continental Drift enabled global circulations and faunal interchanges via dispersals among Mesozoic marine reptiles, others parameters, such as ecological and biological constraints, probably also played a role in the local endemic distribution of some of these marine groups, as they do today. [less ▲]

Mesosaurus Broom, 1913, from the Early Permian, is the first aquatic reptile known in the fossil record. Its co-occurrence in both South Africa (South Africa) and South America (Brazil, Uruguay) made it ... [more ▼]

Mesosaurus Broom, 1913, from the Early Permian, is the first aquatic reptile known in the fossil record. Its co-occurrence in both South Africa (South Africa) and South America (Brazil, Uruguay) made it one of the key-fossils - with the pteridospermatophyta plant Glossopteris - used by the German meteorologist / geophysician Alfred Wegener to support his theory of the Continental Drift (Kontinentalverschiebung), first published in 1912. But Mesosaurus was only the “tip of the iceberg” as, during the Mesozoic, various clades of reptiles massively invaded the aquatic, and more especially, the marine realm. They were highly diversified both systematically and ecologically, and some of them were large top-predators of the marine ecosystems. The main groups were, in order of appearance in the fossil record, Ichthyosauria (earliest Triassic – early Late Cretaceous), Sauropterygia (nothosaurs, pachypleurosaurs, placodonts, plesiosaurs; Early Triassic – latest Cretaceous), Thalattosauria (Middle-Late Triassic), Pleurosauria (Early Jurassic–Early Cretaceous), as well as, among others, several lineages of Chelonians (e.g. chelonioids, bothremydids, “thalassemyds”), Crocodyliformes (thalattosuchians, dyrosaurids, pholidosaurids, gavialoids) and Squamates (mosasauroids, “dolichosaurs”, marine snakes). During the Mesozoic, the palaeobiogeographical distributions and the dispersion events of these marine reptiles closely followed the break-off of the Pangea induced by plate tectonic movements. Although marine reptiles can help in determining the possible date of opening of marine corridors, the information they provide are less precise than that delivered by terrestrial faunas, as the marine realm is a more open system and various migration ways are always possible. Generally, the Triassic taxa were animals with a restricted palaeobiogeographical distribution living near the coastlines of the Pangea. From the end of the Triassic and during the Jurassic, the break-off of the Pangea resulted in the formation of large marine corridors, allowing open-sea marine reptiles such as ichthyosaurs, plesiosaurs and crocodyliformes to spread out over large distances. As an example, similar marine reptile faunas are known from the Jurassic of Europe and southern South America, as a result of dispersion events via the Hispanic Corridor that connected the Tethys / North Atlantic and Pacific realms at this time. During the Cretaceous, and notably with the expansion of the Atlantic Ocean, most of these reptiles were cosmopolite and open-sea forms (plesiosaurs, mosasaurid squamates, chelonioid turtles). However, even if large faunal interchanges were possible, some provinces such as the Northern and Southern margins of the Tethys were characterized by a peculiar faunal identity, notably concerning mosasaurids, despite the apparent absence of barriers. So, if Continental Drift enabled circulation and faunal interchanges, other parameters such as ecological constraints probably also played a role in the distribution of these marine reptile faunas. [less ▲]